What is the normal function of the STAMBP gene?

The STAMBP gene provides instructions for making a protein called STAM binding protein. Although its exact function is not well understood, within cells this protein interacts with large groups of interrelated proteins known as endosomal sorting complexes required for transport (ESCRTs). ESCRTs help transport proteins from the outer cell membrane to the interior of the cell, a process known as endocytosis. In particular, they are involved in the endocytosis of damaged or unneeded proteins that need to be broken down (degraded) or recycled by the cell. ESCRTs help sort these proteins into structures called multivesicular bodies (MVBs), which deliver them to lysosomes. Lysosomes are compartments within cells that digest and recycle many different types of molecules.

Through its association with ESCRTs, STAM binding protein helps to maintain the proper balance of protein production and breakdown (protein homeostasis) that cells need to function and survive. Studies suggest that the interaction of STAM binding protein with ESCRTs is also involved in multiple chemical signaling pathways within cells, including pathways needed for overall growth and the formation of new blood vessels (angiogenesis).

How are changes in the STAMBP gene related to health conditions?

At least 13 mutations in the STAMBP gene have been identified in people with microcephaly-capillary malformation syndrome, an inherited disorder characterized by an abnormally small head size (microcephaly), profound developmental delay and intellectual disability, recurrent seizures (epilepsy), and abnormalities of small blood vessels in the skin called capillaries (capillary malformations).

The known STAMBP gene mutations reduce or eliminate the production of STAM binding protein. This shortage allows damaged or unneeded proteins to build up inside cells instead of being degraded or recycled, which may damage cells and cause them to self-destruct (undergo apoptosis). Researchers suspect that abnormal apoptosis of brain cells starting before birth may cause microcephaly and the underlying brain abnormalities found in people with microcephaly-capillary malformation syndrome. A lack of STAM binding protein also alters multiple signaling pathways that are necessary for normal development, which may underlie the capillary malformations and other signs and symptoms of the condition.

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